The present invention relates to improved double-hull tanker construction, and particularly to construction of such a tanker in which the longitudinal midbody is provided along the centerline of each of its modules, with a respective portion of a keel structure-double hull structure-pipe tunnel subassembly which has been preconfigured with longitudinal and branch cargo and ballast piping, including associated valves and fittings, instrumentation and hydraulic control piping and valves, pipe tunnel ventilation ducts, walkways and other miscellaneous equipment required for routine operation and or maintenance.
The U.S. patent of Cuneo et al., U.S. Pat. No. 5,085,161, issued Feb. 4, 1992, discloses a method and apparatus for constructing a double-hull tanker having a minimum of transverse structure. A series of longitudinal midbody double-hull modules is produced, each in an up-ended orientation which facilitates automated welding of joints at respective sets of proximally arranged plate edges, cleaning and coating of the modules, which are then turned horizontal and serially joined to provide a longitudinal midbody. Prefabricated bow and stern sections are joined to opposite ends of the midbody, and the tanker is completed by installing remaining structural and nonstructural components including piping, valving and wiring. In the Cuneo et al. patent, the vessel hull is shown provided along the centerline of the midbody, with a box-shaped centerline keel structure having its outer and inner sides respectively coincident with the outer and inner hulls of the double-hulled vessel.
The U.S. patent of Goldbach et al., U.S. Pat. No. 5,090,351, issued Feb. 25, 1992, discloses additional details of such a method, apparatus and hull construction, incidentally including a longitudinal bulkhead which divides the cargo space in each module to two side-by-side tanks. In that instance, a structure similar to the box keel structure is illustrated in the same relative location, and forming a base for the longitudinal bulkhead.
Details of construction of the longitudinal bulkhead units of a double-hull tanker, wherein the box keel portions can be fabricated and installed as respective base portions of the longitudinal bulkhead units are disclosed in the U.S. patent of Goldbach et al., U.S. Pat. 5,086,723, issued Feb. 11, 1992.
Various improvements and elaborations upon the mechanical design and construction of such double-hulled tankers and longitudinal midbody modules thereof, are disclosed in Goldbach et al., U.S. Pat. No. 5,269,246, issued Dec. 14, 1993, Goldbach, U.S. Pat. No. 5,320,055, issued Jun. 14, 1994, Goldbach, U.S. Pat. No. 5,293,830, issued Mar. 14, 1994, Goldbach et al., U.S. Pat. No. 5,313,903, issued May 24, 1994, Goldbach copending U.S. patent application No. 08/264,152, filed Jun. 22, 1994, and Goldbach copending U.S. patent application No. 08/281,000, filed Jul. 27, 1994.
Individual cargo and ballast tanks in oil tank vessels are typically outfitted with a considerable amount of equipment, piping and nonstructural components necessary for the safe and efficient carriage and transfer of oil cargos and ballast. In conventional tanker design and construction, this outfit is installed in various structural subassemblies and at various times in the construction schedule.
As a result, some components are installed in the cargo and ballast tanks, making them relatively inaccessible for inspection, maintenance and routine operation. Some may be installed between the hulls, where progressive flooding through piping or through a between-hulls pipe tunnel may adversely impact on survivability of the vessel after bottom damage. Further, incremental installation of these components during construction of the vessel (in contrast to during in-shop-fabrication of subassemblies), leads to variability in layout, inaccessibility of some components, and to damage to surface coatings which gives corrosion early sites to begin attack, and/or to the need for extensive recoating efforts to be expended.